1. Field of the Invention
The present invention relates to a process for the production of magnetoresistive sensors. The process of the present invention makes it possible, in particular, to facilitate a collective production of these sensors.
2. Discussion of the Background
Structures using magnetoresistive effects are used in various fields, particularly in the field of magnetic recording, to detect a magnetic field placed on a support such as, for example, a tape or magnetic disk. These magnetoresistive sensors make it possible to be free of the limitations attached to inductive methods, particularly the requirement for a relatively high speed of advance of the magnetic tape in relation to the magnetic reading head.
In magnetoresistive sensors, a phenomenon is used in which the value of the ohmic resistance of certain materials varies as a function of the magnetization which prevails there This variation of resistance is detected using ordinary methods, for example, by detecting or measuring variations of intensity of an electric current.
The magnetoresistive sensors comprise an actual magnetoresistive element through which a measuring electric current passes. The magnetoresistive elements are made in such a way that the magnetic fields to be measured are perpendicular to the easy magnetization axis of the material and that the current passes parallel to this axis.
A constant so-called "polarization" magnetic field which causes the magnetization to rotate in relation to the easy axis can advantageously be added so that the variation of resistance is, on one hand, maximum and, on the other hand, linear as a function of slight field variations. This "polarization" can be caused in various known ways: for example, with a strong coercive field layer; or else using a current in a conductor close to the sensor; or else with a magnetically antiferromagnetic layer coupled to a sensitive resistor.
Other arrangements can further be made, particularly within the framework of magnetic recording where a very great space resolution is desired, arrangements which consist, for example, in producing layers of shielding on both sides of the magnetoresistive element.
Magnetoresistive elements are currently made of alloys such as, for example, permalloy (Fe.sub..perspectiveto.80 Ni.sub..perspectiveto.20). Detailed explanations concerning the magnetoresistive effect and the making of magnetoresistive sensors can be found in an article by D. THOMPSON published in IEEE Transaction on Magnetics, vol. 11, No. 4, 1975, page 1039.
The various embodiments mentioned above are all more or less compatible with collective production methods. These methods use, in particular, thin layer film technologies and microlithography techniques, on a substrate common to a large number of magnetoresistive sensors. Thus, it is possible to greatly reduce costs, both for "individual" magnetoresistive sensors intended to operate individually after having been separated from the other sensors, and for sensors intended to be associated in operation and, for example, to form the elementary magnetic heads of a multitrack reading head.
Generally, the various production stages are common to all of the sensors formed on the same substrate, up to a polishing stage. The polishing stage has as its object, in particular, to define in a precise way a dimension (length or width) of the magnetoresistive elements. In the case, for example, where sensors arranged in rows and columns are made on the same substrate, it is necessary to cut the substrate into strips (along the rows or columns) and to polish the edges of the strips to define the edges of all the magnetoresistive elements carried by the strip. In the case of magnetic reading heads, the edges thus polished of the magnetoresistive elements are oriented toward the magnetic support to be read.
This polishing operation, thus performed strip by strip, constitutes a long, delicate and therefore costly operation.
Further, in the case of a matrix arrangement of magnetoresistive sensors (for a multitrack reading head, for example), it is necessary to add an operation of assembly of the various strips after polishing, whereas microlithography techniques make it possible to make rows and columns of sensors directly at the desired pitches.